(1) Field of Invention
The present invention relates to the field of radio transmissions, specifically technology for launching digitally synthesized, broad-band, multi-function signals that propagate as radio-frequency (RF) waves.
(2) Description of the Prior Art
It is known in the art that the air interface properties of gain and effective aperture are related to each other by a defined ratio. If the effective aperture is increased by a factor of two; the gain will also increase by a factor of two.
The effective aperture of a “transmitting” White Nail Eplane of the present invention (referencing the baseline of the Steinbrecher patents below) is equal to the product of the number of transmitting “Epixels” and the effective aperture of one Epixel. Thus, when the number of transmitting Epixels is doubled; the gain increases by a factor of two so that the Effective Isotropic Radiated Power (EIRP) of the transmitter is increased by a factor of four. First, the input power to the aperture is doubled because the number of transmitting Epixels is doubled because the number of transmitting Epixels is doubled, and, second, the aperture gain is doubled because the effective aperture is doubled. The result is that the far-field spatially combined EIRP (which is the product of the input power and the gain) increases by a factor of four. In this transmitting mode, a fully populated Eplane emulates a digital-to-analog converter (DAC) because each Epixel emulates one Voltage Least Significant Bit (VLSB).
In order to better understand the White Nail architecture in regard to the transmitter mode; it is necessary to note the operation of the conventional digital-to-analog converter (DAC). The output voltage of a 8-bit DAC comprises 2exp(8) or 256 VLSBs. Thus, an Eplane with 256 Epixels can emulate in the spatially-combined far field the performance of an 8-bit DAC. However, in actual practice, only 128 Epixels are necessary to emulate an 8-bit DAC in the spatially combined far field because the phase associated with each Epixel can be either UP or DOWN, which is a difference of 180 degrees.
The output of a DAC is an output voltage that is dependent on the digital “word” applied to the input. The output voltage is measured in VLSB. Thus, the output voltage of an 8-bit digital-to-analog converter will comprise a voltage staircase with 256 steps—each of which is equal to one VLSB.
The staircase concept is commonly used to describe quantized voltage signals in that there is a one-to-one correspondence between an input digital word and a specific step on the staircase. The voltage staircase generally extends in positive and negative directions from zero. For example, consider a 4-bit DAC in which 0000 results in an output voltage of 0 Volts and in which the left most bit is a “sign bit”.
In further description, 1001 results in an output voltage of +1 VLSB and 0001 results in an output voltage of −1 VLSB. Similarly, 1010 and 0010 results in +2 VLSB and −2 VLSB respectively; 1011 and 0011 results in +3 VLSB and −3 VLSB and so on up to 1111 and 0111 corresponding respectively to +7 VLSB and −7 VLSB. Thus, the staircase has fourteen steps and the peak-to-peak output voltage of the DAC is 14 VLSB. One bit is reserved for the sign bit and zero VLSB is assigned to both 1000 and 0000.
By using this code assignment, the sign bit determines the phase of a RF signal applied to a plurality of Epixel amplifiers with the remaining bits determining how many Epixels will be energized to achieve that level of the staircase in the far field of the White Nail Eplane. Since the instantaneous output is measured in Volts, the instantaneous power delivered to the analog stage is proportional to the square of the number of VLSBs present at this instant. As will be shown, a property related to the White Nail transmitter is that the instantaneous EIRP in the far field of the transmitter is proportional to the square of the number of energized Epixels at that instant.
The following patents and patent applications referenced by the inventor, Dr. Don Steinbrecher, support the structure and operation of the present invention.
U.S. Pat. No. 6,466,167 B1, entitled ANTENNA SYSTEM AND METHOD FOR OPERATING SAME, teaches digital signal processing algorithms that are used to create digital images using the energy segments captured by the White Nail partitioned air interface. A method using an observable signal injected into the signal paths describes a means for phase alignment across the partitioned White Nail air interface—known as an Eplane. The patent discloses an antenna apparatus comprising an array of partition elements that form a plurality of effective aperture segments. The patent describes a system operating in a receive mode to capture RF signals incident on the air interface of the antenna apparatus. An observable signal containing a low-frequency component and a high-frequency component is generated and injected into the signal path associated with each Epixel. The observable signal passes through the same signal path as the RF energy captured by the associated Epixel and can later (in the digital process) be used to establish a phase reference at the phase center of each Epixel for the RF energy captured by that Epixel. In this way, the energy captured by a plurality of Epixels can be reassembled in the digital domain as representative of the RF energy incident on the air interface containing the plurality of Epixels.
U.S. Pat. No. 7,250,920 B1, entitled MULTI-PURPOSE ELECTROMAGNETIC RADIATION INTERFACE SYSTEM AND METHOD, teaches the method for using the partitioned White Nail air interface in applications where the radar cross-section of the air interface is a system parameter. The patent discloses an electromagnetic radiation interface system that is suitable for use with propagating radio waves. A surface is provided with pluralities of electrically-conductive partition elements that are sometimes referred to as “bristles”. The partition elements form a plurality of small effective apertures that are referred to as Epixels. Each Epixel captures a portion of the incident-propagating electromagnetic waves. Each energy portion captured by an Epixel is coupled to a transmission line that is associated with that Epixel and thereby forms the beginning of a signal path that is unique to one Epixel. At some point in the signal process, each unique signal path passes through a single analog-to-digital converter; thereby forming a plurality of digital signal data streams equal in number to the number of Epixels in the partitioned White Nail interface.
U.S. Pat. No. 7,420,522 B1, entitled ELECTROMAGNETIC RADIATION INTERFACE SYSTEM AND METHOD, teaches the partitioned White Nail air interface concept and method for determining the properties of the partitioned energy capture areas. The patent discloses an energy-efficient system for RF signal acquisition that is described as a software-defined air-interface system. The technology of the system is also referred to as White Nail. The White Nail system utilizes partition elements that partition the air interface, which is called an Eplane into a plurality of segments called Epixels which are used to capture portions of RF signals that are incident on the air interface. The portions of the RF signals that are captured by the Epixels are processed individually and may be reassembled in the digital domain to create a digital image of the incident RF signal set. When the White Nail air interface is used in a transmit mode to launch electromagnetic waves, each Epixel is created separately and then transmitted independently. The Epixel signals are collectively combined in the far field to form a radio-frequency beam.
U.S. application Ser. No. 13/134,957 entitled METHOD FOR ENABLING THE ELECTRONIC PROPOGATION MODE TRANSITION OF AN ELECTROMAGNETIC INTERFACE teaches a method used by the partitioned White Nail air interface to capture the signal segments that are created by the partitions. Typically, a White Nail Eplane may be partitioned into one hundred Epixels, each of which has two RF ports where the two orthogonal polarization vector components appear. These two hundred signal components are captured by two hundred balanced transmission lines that connect the signals to circuits that process the signals.
Specifically, the patent discloses a propagating mode transition system that provides a transition from a free-space-propagating electromagnetic energy field, which is partitioned by an array of elongate elements, to a transverse electromagnetic-mode propagating energy field in a balanced transmission line. Electrically-conductive pads are disposed on a substrate with the pads being arranged in spaced-apart fashion. Each pad is substantially covered by and electrically coupled to one of the elongate elements at a base thereof such that portions of each pad not covered by the base are exposed. Each of a plurality of transmission line baluns extends through the substrate with one end thereof disposed between the exposed portions of two adjacent pads. Each balun includes two identical-width electrical conductors with each conductor being electrically coupled to one of the exposed portions.
U.S. application Ser. No. 13/236,871 entitled INTERFACE BOARD CONNECTOR, improves upon the previous reference (U.S. application Ser. No. 13/134,957) in that a interface connector is claimed that will allow removal and replacement of the signal capture boards so that electronic circuits can be placed directly on the signal capture boards. This greatly increases the potential applications and significantly improves the performance of the White Nail capture system.
Specifically, the patent discloses an interface board connector includes a plurality of individual conductive partition element seats. Each partition element seat includes four spring fingers that extend into apertures in a dielectric base plate. Two adjacent spring fingers form a tweezers-like connector in one of the apertures that couples to a trace on a balun board contact post to form an impedance-matched extension of the balanced transmission line that is an integral part of the adjacent partition element seats. Each spring finger includes distinct sections. A ramp section allows the balun board, when inserted, to push apart the spring fingers and slide into place. The contact sections of two adjacent spring fingers form the electrical junction between the balanced transmission line traces on the balun board contact post and the section of balanced transmission line formed by the parallel spring sections of the two adjacent spring fingers.